Sunscreen compositions are typically used in sunny places. Consumers wearing sunscreen products are typically engaging in outdoor activities such as running and swimming. This makes sunscreen products constantly in contact with water and/or sweat. A key parameter in the development of anhydrous sprayable sunscreen is the ability to make such products hydrophobic so that their residence on skin is extended. Another key parameter relates to the development of sunscreen formulations having increased sun protection factor (SPF) values.
Non-aqueous sunscreen sprays have been increasing in popularity in the U.S. over the last few years. The composition of these sunscreen products is essentially based on the concept of dissolving the active ingredients (Sunscreens) in alcohol and adding a hydrophobic polymer to the products to make them water resistant. Additives such as boosters, preservatives, emollients, fragrance and skin conditioning agents may be added to such formulations. The addition of hydrophobic polymers to the skin may not be very pleasing to wear on the skin all day. Especially upon re-application, several coats of the hydrophobic polymer will accumulate and might be more uncomfortable to wear.
Hydrophobic polymers typically have been used to impart water proofing onto formulations. The hydrophobic polymers do not change their conformation upon exposure to water but stay unchanged as depicted in FIG. 1.
Higher SPF products are desirable to provide higher UV protection. One way of achieving higher SPF values is to increase the amount of sunscreens in the product. However, this approach will increase the cost of the product and might negatively impact the sensory characteristics of the product.
Currently, the main pathway to achieving high SPF values is to increase the UV absorbers to maximum allowable concentrations. Small amounts of UV absorbers, like butyl octyl salicylate, have also been added as boosters to formulations. SPF has also been increased by adding light scattering/refracting polymers to the product such as styrene/acrylates copolymers. In addition, in some instances, certain polymers like Tricontanyl PVP have been used to increase the SPF of the formulation (see U.S. Pat. No. 6,436,376).
A few film formers have the ability to boost the SPF of a formulation. The mechanism is generally attributed to the ability of the polymer to make a uniform film of the product onto the skin. The distribution of the sunscreen actives in the film is considered key to the boosting effect of such polymer. In addition, the uniformity of the film is also of great importance. Since the surface of the skin is really not very uniform, many polymers do not have the ability of forming continuous films on the skin. That is why not all film formers are considered SPF boosters. The ability to identify such classes of polymers is key to achieve higher SPF values with less sunscreen in the formulations.